444 Wortman — Studies of Eocene Mammalia in the 



has developed a more perfect shearing apparatus and the inter- 

 nal cusp has been reduced .; in the inferior series, the sectorial 

 has been modified into a more perfect shearing organ bj the 

 enlargement and lateral flattening of the two external cusps of 

 the trigon, by their more perfect alignment with the long 

 axis of the jaw, with a concomitant reduction in size of the inter- 

 nal cusp, the disappearance of the posterior shear and the 

 widening of the heel ; the cusps of the posterior molars have 

 been reduced and their tuberculo-sectorial pattern lost ; in 

 the atlas the alee have increased in size and have developed a 

 peculiar and characteristic arrangement of the foramina for 

 the passage of the vertebral artery ; the lumbar vertebrae have 

 been greatly reduced in size in comparison with the dorsals ; the 

 ischial tuberosities have increased in size, the body of the ischium 

 has become shortened and the obturator foramen reduced ; 

 the femur has been lengthened, the shaft has developed an 

 antero-posterior curvature, the neck of the bone elongated, the 

 lesser trochanter reduced in size and the third trochanter has 

 disappeared ; the tibia has been lengthened, the cnemial crest 

 shortened and the distal trochlea deeply grooved ; the shaft 

 of the fibula has been reduced to a thin lamella of bone which 

 has become applied to the shaft of the tibia for a large part of 

 its extent; the hind foot has been compressed and greatly 

 elongated, the astragalus deeply grooved, and the navicular 

 narrowed ; the metatarsals have become proximally flattened, 

 closely appressed and have developed a characteristic "square- 

 cut" appearance of the distal ends; the hallux has disappeared 

 and the internal cuneiform has been reduced to a vestige ; the 

 phalanges have been slightly shortened and those of the 

 middle row have largely lost their distal asymmetry ; in the 

 forelimb the humerus has been elongated, the deltoid crest 

 and supinator ridge greatly reduced, the entepicondylar fora- 

 men has disappeared, the intercondylar perforation formed and 

 the distal end of the bone greatly narrowed ; the ulna and 

 radius have been greatly elongated, and the head of the radius 

 flattened so as to considerably restrict the power of pronation 

 and supination. 



The three species at present known may be distinguished as 

 follows : 



Posterior external angle of first superior molar more 

 or less extended and cutting ; a strong postero- 

 internal cusp . V. palustris 



Posterior external angle of first superior molar 

 rounded ; postero-internal cusp small and consist- 

 ing of no more than a cingulum V. Hargeri 



Species considerably smaller than the two preceding V. parvivorus 



